Use of thionium derivatives as corrosion inhibitors

ABSTRACT

1,2-DITHIOLE - 3 - THIONES, PARTICULARLY THE QUATERNARIES THEREOF (I.E., THIONIUM DERIVATIVES), ARE PARTICULARLY USEFUL AS CORROSION INHIBITORS IN AQUEOUS AND/OR AREATED AND/ OR HIGHLY ACIDIC SYSTEMS. THE YIELDS OF THIONIUM DERIVATIVES ARE INCREASED BY REACTING 1,2-DITHIOLE-3-THIONES WITH QUATERNIZING AGENTS BY REDUCING THE AMOUNTS OF, AND PREFERABLY IN THE SUBSTANTIAL ABSENCE OF, SOLVENTS.

3,697,221 Patented Oct. 10, 1972 United States Patent Oficc 3,697,221USE OF THIONIUM DERIVATIVES AS CORROSION INHIBITORS Derek Redmore,Ballwin, and Bernardus A. Oude Ahn k,

St. Louis, Mo., assignors to Petrolite Corporation, Wilmington, Del. NoDrawing. Filed Jan. 19, 1970, Ser. No. 4,046 Int. Cl. C23f 11/04, 11/16US. Cl. 212.5 6 Claims ABSTRACT OF THE DISCLOSURE 1,2-dithiole 3thiones, particularly the quaternaries thereof (i.e., thioniumderivatives), are particularly useful as corrosion inhibitors in aqueousand/or aerated and/ or highly acidic systems. The yields of thioniumderivatives are increased by reacting 1,2-dithiole-3-thiones withquaternizing agents by reducing the amounts of, and preferably in thesubstantial absence of, solvents.

1,2 dithiole 3 thiones are known compounds prepared by a variety ofmethods. Examples of such compounds, and methods for their preparation,are disclosed in The Chemistry of Heterocyclic Compounds, Multi- Sulfurand Sulfur and Oxygen Fiveand Six-Membered Heterocycles, Part 1, pages237-386, by David S. Breslow et al. Interscience Publishers, 1966.

1,2-dithiole-3-thiones may be expressed by the formula:

from these compounds according to the following reaction:

where R" X is a quaternizing compound.

Examples of quaternaries or thionium derivatives of1,2-dithiole-3-thiones are presented in Table 7 of Breslow et al., pages394-6, which is incorporated by reference into this application as ifpart hereof.

We have now discovered the yield of the quaternaries (or thioniumderivatives of 1,2-dithiole-3-thiones) can be enhanced, by reducing thesolvent or preferably in the substantial absence of solventssubstantially quantitative yields can be obtained as compared to lowyields obtained when prepared in the presence of solvents.

1,2-dithiole-3-thiones are conveniently prepared by the classic methodof reacting an olefin with sulfur, for example, according to thefollowing equation:

The olefin employed in the reaction contains (1) a reactive double bond(2) a primary carbon atom (3) at least four hydrogen atoms on the 3terminal carbons with at least one hydrogen on the carbon beta toprimary carbon atom.

This reaction is carried out at any suitable temperature and time, forexample, at about to 300 C., such as from about to 240 C. but preferablyfrom about to 220 Crfor a period of about 2 to 160 hours, and

about 10 to 50 hours, but preferably about 15 to 40 hours.

The thionium compounds are prepared by reacting the1,2-dithiole-3-thiones with any suitable quaternizing agent at suitabletemperatures and times, such as a temperature of from about 40 to 200C., but preferably from about 50 to 180 C., for a period of about 1 to24 hours, such as about 2 to 15 hours, but preferably 3 to 6 hours.

The following examples are presented by way of illustration and not oflimitation.

EXAMPLE 1 The preparation of 4-phenyl-,2-dithiole-3-thione MethodA.Quaternization of 4 phenyl-1,2-dithiole-3- thione in the presence ofsolvent-isopropanol with a)2 4 A sample of 21.0 g. of4-phenyl-1,2-dithiole-3-thione (Ex. 1) and 12.6 g. of dimethylsulfate(CI-[Q 80 in 180 cc. of isopropanol was refluxed for 24 hours. Afterthis period 4.5 g. of the product was removed by decanting the hotisopropanol solution. After the isopropanol cooled to room temperature,crystallization took place. The crystals, 3 g. were identified asunreacted starting material. Yield was 64%.

Method B.Quaternization of 4 phenyl-1,2-dithiole-3- thione in thepresence of solvent-benzene with a)2 4 A sample of 8.4 g. of4-phenyl-1,2 dithiole-B-thione (Ex. 1) and 5.0 g. of dimethylsulfate in100 cc. of benzene was refluxed for 24 hours. The product was dissolvedin a mixture of 100 cc. H 0 and 10 cc. of acetone. About 1.0 g. ofby-product was formed. Yield was 85%.

EXAMPLE 2 Preparation of 4-(3-methoxy-4-hydroxy)phenyl- 1,2-dithiole-3-thione In a suitable reactor equipped with a stirrer, thermometer,addition funnel and reflux condenser was placed, 32 g. of sulfur, 1.0 g.of di-o-tolylguanidine as catalyst and 150 cc. of mesitylene as solvent.The mixture was brought to a reflux C.) and over a 1 hour period 66 g.of lsoeugenol Ho-Q4m -c1hom was added dropwise. Reflux was continued for48 more hours. The mesitylene was decanted from the solid. The solid wastreated twice with 500 cc. portion of a aqueous potassium hydroxidesolution. Upon acidification the product precipitated as a brown solid.

A 5.2 g. sample of 5-(3-methoxy-4-hydroxy)phenyl-l,2- dithiole-3-thionewas quaternized following Method B, (with benzene as a solvent) theyield was 40%.

Method C.-Quaternization without solvent with (CH SO A 17.0 g. sample of5-(3-methoxy-4-hydroxy)phenyl- 1,2-dithiole-3-thione and 8.5 g. ofdimethyl sulfate were heated for 1 hour at LOO-120 C. After the reactionwas completed 25.5 g. of isopropanol was added to give a homogeneoussolution. Yield was quantitative.

W EXAMPLE 3 Preparation of 4-neopentyl-5-t-butyl-1,2-dithiole-3-thioneTo a mixture of 320 g. of sulfur and 6.0 g. of di-otolylguanidine wasadded over a 9 hour period, at a reaction temperature of 210-215" C.,336 g. of triisobutylene,

Heating at 210-215 C. was continued for an additional 14 hours. Theproduct was distilled and there was collected 220 g.4-neopentyl-5-t-butyl-1,2-dithiole-3-thione, B.P. 155-185 C. (34 mm.Hg).

(CHa)aC CH3- =S Quaternization acording to Method A (with isopropanol assolvent) failed. The use of acetic acid as the solvent in thequaternization was unsuccessful. Method C (without solvent), however,converted 4-neopentyl-5-tbutyl-1,2-dithiole-3-thione quantitatively toits quaternary methosulfate.

Method D.Quaternization of 4-neopentyl-5-t-butyl-1,2- dithiole-3-thionewith methyl iodide employing chloroform as solvent A sample of 3.0 g. of4-neopentyl-5-t-butyl-1,2 dithiole- 3-thione and 6.0 g. of methyl iodidein 50 cc. of chloroform was allowed to stand overnight. The solvent wasremoved and the orange solid washed with isopropanol and benzene, M.P.135-142 C. Yield was 3.8 g. (82%).

EXAMPLE 4 Preparation 4,5-tetramethylene-1,3-dithiole-3-thione MethodA.-Quaternization of 4,5-tetramethylene-l,2- dithiole-3-thione in thepresence of solvent-isopropanol A sample of 11.3 g. of4,5-tetramethylene-1,3-dithiole- 3-thione and 7.6 g. of dimethyl sulfatein 100 cc. of isopropanol was refluxed for 24 hrs. During this timehydrogen sulfide is evolved. After the reaction was completed 5 g. of ahard blue solid crystallized from the solution.

The nuclear magnetic resonance spectrum of the product is consistentwith the following structure:

|SI-OH I \S s The mother liquor contained 50% of 3-S-rnethyl-4,5-tetramethylene-l,2-dithiole-3-thione methosulfate.

The following table presents illustrative 1,2-dithi0le-3- thiones of theformula The radical indicated replaces the Hs in the 4th and/or 5thpositions as indicated.

where R is alkyl such as methyl, etc., and R is hydrogen, alkyl, etc.for example methyl p-toluene sulfonates. (5) Alkyl phosphates, e.g.(MeO) PO, (EtO) PO, etc.

USE IN FLUIDS FOR DRILLING WELLS This phase of the invention relates tothe use of the compounds of this invention as corrosion inhibitors inproducing an improved drilling fluid useful in drilling oil and gaswells.

Fluids commonly used for the drilling of oil and gas wells are of twogeneral types: water-base drilling fluids comprising, for example, aclay suspended in water, and oil-base drilling fluids comprising, forexample, a clay or calcium carbonate suspended in mineral oil.

A third type of drilling fluid which has recently been developed, is oneof oil-in-water or water-in-oil emulsion, for example, emulsions ofmineral oil in water or water in mineral oil formed by means ofemulsifiers such as sulfuric acid: Turkey-red oil; soaps of fatty acids,for example, sodium oleate; emulsoid colloids, for example starch,sodium alginate, etc. Varying amounts of finely divided clay, silica,calcium carbonate, blown asphalt and other materials may be added tothese emulsions to improve their properties and control their weight.

We have now discovered that the compositions of this invention can beemployed as a corrosion inhibitor in drilling fluids.

USE IN AIR DRILLING It has long been conventional practice in drillingdeep bore holes to circulate a drilling *mud down through the drill stemand up through the bore hole between the wall of the bore hole and thedrill stem for the removal of chips or cuttings from the bore hole andto provide support for the wall of the bore hole. More recently, in thedrilling of holes in which wall support provided by drilling mud is notemployed, drilling has been carried out with the use of air for chipremoval. Such drilling is not only normally faster than mud drilling butis indispensable in areas Where the supply of water is limited or whendrilling throu gh cavernous formations into which the drilling mud flowsand becomes lost.

The increasing popularity of air or gas drilling has come about not onlybecause this method of drilling is frequently faster, as noted above,but for the additional reasons that the drill bits last longer, theprovision and handling of water under wide ranges of temperatureconditions is avoided, boring samples are easily observed when they arenot mixed with mud, and there is no loss involved as in the case of muddrilling when drilling through cavernous formations. Furthermore, promptremoval of water entering the hole maintains a dry hole and thelikelihood of wall collapse is thereby reduced.

In a typical air drilling operation there may be provided, for example,an up-fiow of air in the bore hole having a velocity of the order of3,000 feet per minute. This flow of air upwardly through the bore hole,which is produced by air pumped downwardly through the drill stern,provides adequate removal of cuttings. The air is delivered to the drillstem at pressures of 20 to 60 lbs. per square inch and for dewatering orfor breaking obstructions, as will be hereinafter described, thepressures may be increased to 180 to 200 lbs. or more per square inch.

Air drilling operations are frequently hampered by the inflow of waterinto the bore hole when the drill bit is penetrating a water bearingstratum or when the bore hole has passed through a water bearing stratumthat has not been cased. Normally, if drilling proceeds uninterruptedlyboth before and during penetration into a water bearing stratum, theflow of air is suflicient to blow the 'water out of the bore hole alongwith the cuttings and drilling dirt. There are, however, two majorproblems encountered in air drilling when water is entering the borehole. The first problem occurs when there is a small inflow of watersuflicient to cause a dampening of the cuttings which, under certainconditions, will then ballup, clogging and sometimes jamming the drillbit. The second problem is encountered when there is a substantialamount of water remaining in the bottom of the bore hole during drillingcausing a sloughing of the side wall of the bore hole. This lattercondition may arise even though the water entering the bore hole isbeing blown out of the hole as fast as it enters. If there is asubstantial inflow of water or if there is a substantial flow of waterpast a region of the bore hole susceptible to this condition, the waterpassing that region of the bore hole may cause a slomghing of the sidewall.

The addition of foam forming materials to the air flow when air drillingis employed in conjunction with sufficient water to provide foaminggives rise to numerous advantages in drilling operations. The water maybe introduced either through a water bearing stratum being penetrated bythe drill bit or, alternatively, if the hole is dry, water may beintroduced from the surface of the earth through the drill stem inconjunction with the delivery of compressed air and foam formingmaterial through the drill stem to the drill bit. In either case thewater may be said to be existing in the bore hole, and drillingoperations are described in US. Pat. 3,130,798.

The compositions of this invention can be employed as a corrosioninhibitor in a drilling system.

The compositions of this invention may also be added to other aqueousand/or oxygenated systems such as steam generating systems, watercirculating systems such as in cooling towers, in automobile radiators,in diesel locomotive engines, in boiler water, sea-water ship ballast,etc.

The amount of the compositions of the invention to be employed as acorrosion inhibitor can vary widely depending upon particular compounds,the particular system, the amounts of oxygen present, etc. We may employconcentrations of from about 0.5 to 5,000 p.p.m., such as from about 4to 4,000 p.p.m., for example from about 20 to 2,000 p.p.m., butpreferably from about to 1,000 p.p.mf The optimum amount, to bedetermined in each instance, which will depend on function andeconomics, can be lesser or [greater than the above amounts under properconditions.

USE IN BRINES This phase of the invention relates to the prevention ofcorrosion in systems containing a corrosive aqueous medium, and mostparticularly in systems containing brines.

More particularly, this invention relates to the prevention of corrosionin the secondary recovery of petroleum by water flooding and in thedisposal of waste water and brine from oil and gas wells. Still moreparticularly, this invention relates to a process of preventingcorrosion in water flooding and in the disposal of waste water and brinefrom oil and gas wells which is characterized by injecting into anunderground formation an aqueous solution containing minor amounts ofcompositions of this invention, in suflicient amounts to prevent thecorrosion of metals employed in such operation. This invention alsorelates to corrosion inhibited brine solutions of these compounds.

When an oil well ceases to flow by the natural pressure in the formationand/or substantial quantities of oil can no longer be obtained by theusual pumping methods, various processes are sometimes used for thetreatment of the oil-bearing formation in order to increase the flow ofthe oil. These processes are usually described as secondary recoveryprocesses. 'One such process which is used quite frequently is the waterflooding process wherein water is pumped under pressure into what iscalled an injection well and oil, along with quantities of water, thathave been displaced from the formation, are pumped out of an adjacentwell usually referred to as a producing well. The oil which is pumpedfrom the producing well is then separated from the water that has beenpumped from the producing well and the water is pumped to a storagereservoir from which it can again be pumped into the injection well.Supplementary water from other sources may also be used in conjunctionwith the produced water. When the storage reservoir is open to theatmosphere and the oil is subject to aeration this type of waterflooding system is refererd to herein as an open water flooding system.If the water is recirculated in a closed system without substantialaeration, the secondary recovery method is referred to herein as aclosed water flooding system.

Because of the corrosive nature of oil field brines, to economicallyproduce oil by water flooding, it is necessary to prevent or reducecorrosion since corrosion increases the cost thereof by making itnecessary to repair and replace such equipment at frequent intervals.

We have now discovered a method of preventing corrosion in systemscontaining a corrosive aqueous media, and most particularly in systemscontaining brines, which is characterized by employing the compositionsof this invention. V 7 H We have also discovered an improved process ofprotecting from corrosion metallic equipment employed in secondary oilrecovery by water flooding such as injection wells, transmission lines,filters, meters, storage tanks, and other metallic implements employedtherein and particularly those containing iron, steel, and ferrousalloys, such process being characterized by employing in water floodoperation the compositions of this invention.

This phase of the invention then is particularly concerned withpreventing corrosion in a water flooding process characterized by theflooding medium containing an aqueous or an oil field brine solution ofthese compounds.

In many oil fields large volumes of water are produced and must bedsiposed of where water flooding operations are not in use or wherewater flooding operations cannot handle the amount of produced water.Most states have laws restricting pollution of streams and land withproduced waters, and oil producers must then find some method ofdisposing of the waste produced salt water. In many instances therefore,the salt water is disposed of by injecting the water into permeable lowpressure strata below the fresh water level. The formation into whichthe water is injected is not the oil producing formation and this typeof disposal is defined as salt water disposal or waste water disposal.The problems of corrosion of equipment are analogous to thoseencountered in the secondary recovery operation by water flooding.

The compositions of this invention can also be used in such waterdisposal wells thus providing a simple and economical method of solvingthe corrosion problems encountered in disposing of unwanted water.

Water flood and waste disposal operations are too well known to requirefurther elaboration. In essence, in the 10 concentrations, they enhancethe success of a flood operation by lowering the cost thereof.

In addition, these compounds are not sensitive to oxygen content of thewater and these are effective corrosion inhibitors in both open waterflooding systems and closed water flooding systems.

While the flooding medium employed in accordance with the presentinvention contains water or oil field brine and the compounds, themedium may also contain other materials. For example, the floodingmedium may also contain other agents such as surface active agents ordetergents which aid in wetting throughout the system and also promotethe desorption of residual oil from the formation, sequestering agentswhich prevent the deposition of calcium and/or magnesium compounds inthe interstices'o'f the formation, bactericides which prevent theformation from becoming plugged through bacterial growth, tracers, etc.Similarily, they may be employed in conjunction with any of theoperating techniques commonly employed in water flooding and waterdisposal processes, for example five spot flooding, peripheral flooding,etc., and in conjunction with other secondary recovery methods.

Corrosion tests were made using sand blasted 1020 mild steel couponsmonitored by a polarization resistance meter, a Pair instrumentdescribed in U .5. Pat. 3,406,101. These tests were made in cylindricalcontainers of 1500 cc. volume with provision for constant stirring bymeans of a motor driven impeller. A thermostatically controlledimmersion heater maintained an average temperature of 75 C. and an airinlet kept the fluids constantly saturated with air. Between each testthe cylinder was cleaned with steam, benzene, acetone and thoroughlywashed with clean water. Results of these corrosion tests made invarious aqueous environments are shown in the following table.

Protection is calculated in the usual manner from corrosion rate (R offluids without inhibitor and corrosion rate (R in presence of particularinhibitor according to the formula 4.2% NaCl, 1.75% MgCl 0.15% CaCl-0.09% Na SO Table II gives the values for continuous aerated hot (75 C.)brines.

X 100: Percent protection TAB LE II Time, Percent Compound P.p.m. hrs.protection Example 4- 3-S-methyl-4.E-tetramethylene-l,Z-dlthiole-B-thlone-rnethosulfate 1, 000 21 97 3-Smet.iv1*4-phenyl-1.2-d1thiole-3-thione-methosullate H 1, 000 21 513-S-methyl-5(3-methoxy-4-hydroxy1)-pheny1-l,Q-dithiole-3-thione-methosulfat1, 000 21 983-S-rnethyl-4-neopentyl-5-t-butyl-l,2-dithiole3thione-methosulfate 1,000 21 98 Mercaptobenzothiazole 1, 000 21 30 Commercial imidazollne 1,000 21 6 present process, the flooding operation is effected in theconventional manner except that the flooding medium contains a minoramount of the compound of this invention, suflicient to preventcorrosion, in concentrations of about 10 p.p.m. to 10,000 p.p.m., ormore, for example, about to 5000 p.p.m., but preferably about 15 to1,500 p.p.m. The upper limiting amount of the compounds is determined byeconomic considerations. Since the success of a water flooding operationmanifestly depends upon its total cost being less than the value of theadditional oil recovered from the oil reservoir, it is quite importantto use as little as possible of these compounds consistent with optimumcorrosion inhibition. Optimum performance is generally obtainedemploying about 1,000 p.p.m. Since these compounds are themselvesinexepnsive and are used in low USE IN ACID SYSTEMS The compounds ofthis invention can also be employed as corrosion inhibitors for acidsystems, for example as illustrated by the pickling of ferrous metals,the treatment of calcareous earth formation, etc., as described in thefollowing sections.

USE AS PICKLING INHIBITORS oxide coating, formed during manufacturing,from the surface. The presence of oxide coating, referred to as scale isobjectionable when the material is to undergo subsequent processing.Thus, for example, oxide scale must be removed and a clean surfaceprovided if satisfactory results are to be obtained from hot rolledsheet and strip in any operation involving deformation of the product.Similarly, steel prepared for drawing must possess a clean surface andremoval of the oxide scale therefrom is essential since the scale tendsto shorten drawing-die life as well as destroy the surface smoothness ofthe finished product. Oxide removal from sheet or strip is alsonecessary prior to coating operations to permit proper alloying oradherence of the coating to the ferrous metal strip or sheet. Prior tocold reduction,

it is necessary that the oxide formed during hot rolling be" completelyremoved to preclude surface irrgularities and enable uniform reductionof the work.

The chemical process used to remove oxide from metal surfaces'isreferred to as pickling. Typical pickling processes involve the use ofaqueous acid solutions, usually inorganic acids, into which the metalarticle is immersed. The acid solution reacts with the oxides to formwater and a salt of the acid. A common problem in this process isoverpickling which is a condition resulting when the ferrous metalremains in the pickling solution after the It is well known thatproduction of petroleum or gas from a limestone, dolomite, or othercalcareous-magnesian formation can be stimulated by introducing an acidinto the producing well and forcing it into the oil or gas hearingformation. The treating acid, commonly a mineral acid such as HCl, iscapable of forming water soluble salts upon contact with the formationand is effective to increase the permeability thereof and augment theflow of petroleum to the producing well.

The corrosion inhibitors were evaluatedusing sand blasted 1020 mildsteel coupons monitored by a polarization resistance meter, a Pairinstrument described in US. Pat. 3,406,101.

The acid was placed in a beaker and the coupons placed in the acid.Corrosion rates were measured at various time intervals and percentprotection calculated in the usual manner as follows:

Percent protection: X 100 Where R is corrosion rate without inhibitor Ris corrosion in presence of inhibitor.

The utility of the compositions of this invention is illustrated in thefollowing table.

TABLE III.-USE AS CORROSION INHIBITORS IN HIGHLY ACID SYSTEMS Time,Percent Compound D-D-m- Acid min. protection Example:

4 3-S-methyl4,5-tetrarnethylene-1,2 dithiole-3-thione methosnlfate- 1,000 H2804 240 99 6 1 3-S-methyl-4-phenyl-L2 dithiole thione methosulfate500 20% H2304 78 94. 0 1 .do 1,000 85% phosphoric acid 99. 8 1.. "do1,000 85% phosphoric acid; 10% HF... 99. 5 4S-methyl-4,5-tetramethylene-l,2 dithiole-3-thione methosulfate l, 00020% H s 4... 43 99.8 3-S-methyl-4-t-butyl-5-neopentyl-1,2dithiole-S-thione methosu fa 500 20% H2304 45 99, 7 -do ,000 19% HCl. 4399.0

1 18 hours. 2 20 hours.

oxide scale is removed from the surface and the pickling solution reactswith the ferrous base metal. An additional difficulty in picklingresults from the liberated hydrogen being absorbed by the base metal andcausing hydrogen embrittlement. To overcome the aforementioned problemsin pickling, it has been customary to add corrosion inhibitors to thepickling solution.

The present invention avoids the above-described problems in picklingferrous metal articles and provides a pickling composition whichminimizes corrosion, overpickling and hydrogen embrittlement. Thus thepickling inhibitors described herein not only prevent excessivedissolution of the ferrous base metal but eifectively limit the amountof hydrogen absorption thereby during pickling. According to theinvention, a pickling composition for ferrous metal is provided whichcomprises a pickling acid such as sulfuric or hydrochloric acid and asmall but effective amount of the dithiol thione compound of thisinvention, for example at least about 5 p.p.m., such as from about 100to 5,000 p.p.m., but preferably for about 500 to 1,500 p.p.m.

Ferrous metal articles are pickled by contacting the surface (usually byimmersion in the pickling solution) with a pickling composition asdescribed to remove oxide from their surface with minimum dissolutionand hydrogen embrittlement thereof and then washing the ferrous metal toremove the pickling composition therefrom.

USE IN ACIDIZING EARTH FORMATIONS Another important aspect of picklinginhibitors is that they should remain effective in presence of dissolvedferrous ions (from dissolution of the oxide scale). The continuedeffectiveness of the present compositions is illustrated in thefollowing table:

1,2-dithiole-3-thiones and derivatives thereof. Because of theirenhanced solubility in aqueous systems, including brines and acidsystems, the most effective derivative is the thionium derivative.

The amount of 1,2-dithiole-3-thione compound employed in treating thecorrosive systems of this invention will vary with the particularcompound employed, the particular system, the solids present in thesystem, the degree of corrosivity of the system, etc. A minor amount ofthe compound is generally employed sufiicient to impart corrosionprotection to the system. In general one employs concentration of traceamounts such as from about 0.1 p.p.m. to 10,000 p.p.m., for example from5 to 5,000 p.p.m. such as from to 2,500 p.p.m., but preferably from 500to 2,000 p.p.m. In practice, concentrations of 1,000i200 p.p.m., areemployed.

As is quite evident, new 1,2-dithiole-3-thione compounds Will beconstantly developed which could be useful in our invention. It is,therefore, not only impossible to attempt a comprehensive catalogue ofsuch compositions, but to attempt to describe the invention in itsbroader aspects in terms of specific chemical names used would be toovoluminous and unnecessary since one skilled in the art could byfollowing the description of the invention herein select a usefuldithiole-thione compound. This invention lies in the use of suitabledithiolethione compounds as corrosion inhibitors in aqueous and/ oroxygenated and/or acid systems and their individual compositions areimportant only in the sense that their properties can affect thisfunction. To precisely define each specific useful dithiole-thionecompound and aqueous system in light of the present disclosure wouldmerely call for knowledge within the skill of the art in a manneranalogous to a mechanical engineer who prescribes in the construction ofa machine the proper materials and the proper dimensions thereof. Fromthe description in this specification and with the knowledge of achemist, one will know or deduce with confidence the applicability ofspecific dithiole-thione compounds suitable for this invention byapplying them in the process set forth herein. In analogy to the case ofa machine, wherein the use of certain materials of construction ordimensions of part would lead to no practical useful result, variousmaterials will be rejected as inapplicable where others would beoperative. We can obviously assume that no one will wish to use auseless thiole-thione compound nor will be misled because it is possibleto misapply the teachings of the present disclosure to do so. Thus, anythiole-thione or mixtures containing them that can perform the functionstated herein can be employed.

Having thus described our invention what we claim as new and desire toobtain by Letters Patent is:

1. A process of inhibiting corrosion of a metal in a metal corrosivemedium which comprises contacting said metal in said corrosive mediumwith a compound selected from the group consisting of3-S-methyl-4,5-tetramethylene 1,2 dithiole 3 thione methosulfate and 3S- methyl 4 neopentyl 5 t butyl 1,2 dithiole 3- thione-methosulfate.

2. The process of claim 1 wherein the compound is3-S-methyl-4-neopentyl-5-t-butyl-1,2 dithiole 3 thionemethosulfate.

3. The process of claim 2 wherein the corrosive medium is an aqueousbrine system.

4. The process of claim 2 wherein the corrosive medium is an aqueoussystem in the presence of air.

5. The process of claim 2 wherein the corrosive medium is an acidsystem.

6. The process of claim 5 wherein the acid system is an aqueous acid.

References Cited UNITED STATES PATENTS 2,742,369 4/ 1956 Hatch 21-2.5 UX2,816,075 12/1957 Fields 252395 X 2,905,696 9/1959 Fields 252395 X2,912,386 11/1959 Salzberg 252395 3,374,112 9/1966 Blomstrom 252--395 X3,345,380 10/ 1967 Hodgson 252395 X 3,350,408 10/1967 Hodgson 252395 X3,394,146 7/1968 Hodgson et al 252395 X 3,444,163 5/1969 Smutny 260327 CX 3,457,185 7/1969 Betty et a1. 252395 X FOREIGN PATENTS 1,038,8669/1958 Germany 252395 BARRY S. RICHMAN, Primary Examiner US. Cl. X.R.

